Commercial semiconductor foundries often limit designers to a few choices of materials or number of structural layers in a fabricated device. As a result it may not be possible to create many specialized devices required for demanding semiconductor or Micro Electro Mechanical Systems (MEMS) applications without custom fabrication methods, methods that are usually expensive to employ. As an alternative, highly complex structures can be made by flip-chip bonding of surface-micromachined features onto a variety of other substrates or even other chips fabricated in the same process. The original often silicon host substrate is then discarded during a following release etch to provide for example, advanced MEMS devices that are suitable for RF, microwave, or optical applications where specific material properties or additional structural layers are required.
In recent years, the use of flip-chip assembly to create advanced MEMS devices has been shown to be a fast, reliable, simple and inexpensive method to produce highly planarized devices consisting of as many as five structural layers on virtually any desired substrate. This process has been demonstrated with a variety of micromirror arrays and variable capacitors fabricated atop ceramic substrates to achieve improved RF characteristics. Even more advanced micromirror arrays have been fabricated atop receiving modules prefabricated in a same processing run as the host module. Numerous styles of cantilever, torsion, and piston micromirror arrays have been demonstrated and these boast a variety of desirable characteristics. Mirror devices can for example achieve CMOS compatible low voltage addressing potentials or more than 3 micrometers of stable mechanical deflection since the mirror surfaces can rest as much as 10 micrometers above the substrate. Typical arrays have been designed with as much as 98.8% active surface area. Torsion and cantilever devices have demonstrated as much as 20 degrees of tilt using a variety of flexure arrangements to reduce needed electrical addressing potentials. The mirror surface of each such device is initially fabricated as the underside of a first releasable structural layer such that no topographical effects are induced. As a result, flip-chip micromirrors consistently demonstrate less than 2 nanometers of root-mean square surface roughness.
Flip chip bonding of two integrated circuit sized component modules into a MEMS or other single device has however almost universally required each of the component modules to remain on its fabrication substrate or a substitute substrate during the bonding operation. The known few exceptions to this rule involve especially fabricated modules affording some special forms of protection for one module. The present invention changes this situation into one wherein someone with access to the most basic device fabrication capability and its tools can achieve flip chip bonded devices, including devices fabricated on two different and incompatible substrate materials and devices fabricated to include multiple MEMS modules in stacked array. Moreover, the present invention eliminates a significant difficulty in correctly aligning two substrate-mounted modules for bonding. Since the present invention allows use of simple visual alignment procedures it eliminates the need for an expensive piece of measurement-capable fabrication equipment and need for the skilled user to operate this equipment. In direct terms, the present invention is thus concerned with improved off-substrate bonding.
The prior publication and patent art includes numerous examples of hinge and pivot arrangements used for erecting structural elements in an assembled MEMS device or as an active part of the MEMS device function. The concept of using a hinge or pivot as a key part of the assembly or fabrication procedure for a MEMS device, and especially for off chip rotation of substrate-free MEMS modules, appears however to be significantly less well known in the art. Several examples of prior art documents illustrating this state of the MEMS art are included in the references identified with the filing of the present document.
The present invention provides a latching arrangement desirable for use during the flip-chip fabrication of a MEMS device.
It is therefore an object of the present invention to provide a latching arrangement in which simple latching elements are achieved in integrated circuit size elements.
It is another object of the present invention to provide a latching arrangement that is operable by manual manipulation of movable and latching elements.
It is another object of the present invention to provide a MEMS latching arrangement that may be fabricated in silicon semiconductor material or in a variety of other semiconductor art compatible structural materials.
It is another object of the present invention to provide a MEMS latching arrangement in which a multiple structural material layers derived latch element provides movable element arrest and capture during device fabrication.
It is another object of the present invention to provide an external manipulation forces-engageable MEMS latch assembly.
It is another object of the present invention to provide a MEMS latch assembly usable for a variety of MEMS element fixation purposes during and after device assembly.
It is another object of the present invention to provide a MEMS latch assembly that is usable in single or multiple latch environments.
It is another object of the present invention to provide a MEMS latch arrangement employing multiple sliding elements that are held captive.
It is another object of the present invention to provide a MEMS latch arrangement providing inadvertent excessive manual manipulation motion protection for delicate MEMS elements.
It is another object of the present invention to provide a MEMS latch arrangement employing latch elements of unusual multiple layer rigidity and structural integrity.
It is another object of the present invention to provide a captured MEMS latch arrangement involving a first movable element and a second movable element held captive on this first movable element.
It is another object of the present invention to provide a latching arrangement that occupies essentially two-dimensional space in a MEMS device.
It is another object of the present invention to provide a latching arrangement that can be fabricated in the form of overlapped but later segregable MEMS components.
It is another object of the present invention to provide a MEMS latching apparatus inclusive of a positive engagement arrangement with companion MEMS elements.
These and other objects of the invention will become apparent as the description of the representative embodiments proceeds.
These and other objects of the invention are achieved by the hinge and latch method of fabricating an electronically controlled MEMS device comprising the steps of:
forming electronic control circuit module and MEMS active element module portions of said MEMS device on first permanent and second sacrificial substrate members respectively;
said second sacrificial substrate MEMS active element module forming step including providing multiple substrate layers-resident sacrificial supplementary components comprised of a substrate hinge mounted etch plate, etch plate to MEMS active element module connection tethers, a substrate coupled etch plate latch assembly and an etch plate to sacrificial substrate anchor assembly;
releasing said MEMS active element module and selected of said sacrificial supplementary components from forming-related confinement in said substrate multiple layers into movable, hinge mounted to one of said sacrificial substrate and to other of said supplementary components, states;
rotating said released hinge mounted etch plate and tether coupled MEMS active element module combination at said hinge into a selected off of sacrificial substrate position by applying external forces to said etch plate and tethered MEMS active element module combination;
latching said etch plate and tethered MEMS active element module combination into said selected off MEMS substrate rotated position by coupling slidably movable portions of said etch plate latch assembly with said etch plate using external, latch assembly-received, forces;
disposing said MEMS active element module, said tether-attached etch plate, and said hinge mounted MEMS active element sacrificial substrate combination into a position of registered MEMS active element module engagement with said electronic control circuit module; and
engaging said MEMS active element module and said electronic control circuit module into a registered, fixed, device housing-surrounded, electronically controlled MEMS device.